A post mixed burner is a burner wherein fuel and oxidant are delivered in separate passages to a point outside the burner, such as a furnace or other combustion zone, where the fuel and oxidant mix and combust.
A problem in the use of post mixed burners is the operation of a reliable ignition system. Because, in the operation of a post mixed burner the combustible mixture is formed not within the burner but in the combustion zone, the ignition system must be within or close to the combustion zone, thus exposing the ignition system to the harsh environment of the combustion zone. This is especially the case where oxygen is used as the oxidant since oxygen burners typically do not employ a burner block which may provide some protection from the radiant heat of the furnace.
In addition to the problem of reduced reliability due to the high heat resulting from the proximity of the ignition system to the combustion zone, another problem encountered by post mixed burner ignition systems is degradation of the ignition system causing compromised operation.
Generally the ignition system comprises some type of electrical discharge or spark generating device having electric surfaces which must be kept clean in order to operate properly. The proximity of the ignition system to the furnace zone exposes such electric surfaces to corrosive oxidizing atmospheres which create difficulties in maintaining the electric surfaces clean and intact. Moreover, impurities in the fuel may hinder the operation of the ignition system. Such impurities include moisture, which causes corrosion of the electric surfaces and can short the electrode to ground, and particulates, either originally within the fuel or as a result of incomplete combustion, which tend to foul the electric surfaces. Such impurities cause spark generation to be reduced or even totally halted requiring a time consuming and expensive cleaning or replacement of the ignition system.
Accordingly it is an object of this invention to provide a post mixed burner having an ignition system which need not be within or next to the combustion zone and, in addition, can remain free of operation compromising contaminants better than can conventional ignition systems.
It is another object of this invention to provide a method for igniting a post-mixed burner with increased reliability over conventional post mixed burner ignition systems.